1. Field of the Inventions
The present inventions relate to a variable valve train mechanism of an internal combustion engine capable of changing a lift and the like of an intake valve or an exhaust valve of the internal combustion engine.
2. Description of the Related Art
Variable valve train mechanisms have recently been more widely incorporated into mass produced engines. Some variable vale train mechanisms are designed to control lift, and the like, of an intake valve or an exhaust valve of an internal combustion engine according to operating conditions of the internal combustion engine. Such variable valve train mechanisms improve fuel economy and provide steady operating performance under low-load conditions, and can increase intake air charging efficiency to provide sufficient engine output under high-load conditions.
These types of variable valve train mechanisms can include an intermediate driving mechanism or intermediate phase angle changing devices. The intermediate driving mechanism is driven in connection with a rotational cam on a camshaft rotationally driven by a crankshaft of the internal combustion engine, and causes an output portion to drive a valve as an input portion is driven by the rotation cam. The intermediate phase angle changing device changes a relative phase angle between the input portion and the output portion of the intermediate driving mechanism.
The intermediate phase angle changing device can be a helical spline mechanism having a sliding gear with two types of helical splines of different angles and being displaceable in the axial direction of the intermediate driving mechanism, and displacement controller for controlling axial displacement of the sliding gear. The input portion is engaged with one of the two types of helical splines of the sliding gear, and the output portion is engaged with the other.
As the input portion and the output portion are swung relative to the sliding gear according to an axial displacement of the sliding gear through the displacement controller, the input portion and the output portion in engagement with the respective helical splines of different angles of the sliding gear are also swung relative to each other. A relative angle between the input portion and the output portion is thereby changed.
The variable valve train mechanism having an intermediate driving mechanism and the intermediate phase angle changing device allows driving the valve without a long and complex link mechanism between the rotational cam and the intermediate driving mechanism. Further, changing the relative phase angle between the input portion and the output portion can advance and retard the timing of valve opening according to the driving state of the rotational cam. Thus, it is possible to control a lift and the like associated with the drive of the rotational cam (see Japanese Patent Document JP-A-2001-263015, FIGS. 21 and 24 for example.
Other types of variable valve control mechanisms include a rocker arm which abuts and is depressed by a camshaft that rotates in one direction, and an output cam which depresses a solid lifter, connected through a control cam and a control shaft. For example, such a mechanism is described in “A Study of a Mechanical Continuous Variable Rocker Arm (VRA),” by Thitiphol Anontaphan, SAE TECHNICAL PAPER SERIES No. 2003-01-0022; SAE International, USA; Mar. 3, 2003.
In this type of system, a roller is provided at one end of the rocker arm. The roller receives a load from the camshaft, which is then transmitted to an arm of the rocker arm, transmitted to a nose on the opposite side with respect to the control cam, and then transmitted from the nose to the solid lifter via the output cam, so that the lifter is moved upwardly and downwardly.
As the control cam is rotated through the control shaft, a relative angle between the rocker arm and the output cam is changed. Changing the relative angle in such manner allows adjustment of the lift of the solid lifter.
In the type of variable valve train mechanism in which a relative phase angle between the input portion and the output portion of the intermediate driving mechanism is changed by means of the helical spline mechanism as intermediate phase angle changing means so that a lift and the like of the valve is controlled, the helical spline mechanism can swing the input portion and the output portion relative to each other, but has difficulty in controlling a relative phase angle between the input portion and the output portion to a specified angle. Therefore, in some cases, precise control of a valve lift and the opening and closing timing of the valve is difficult to achieve, which results in a problem of difficulty in increasing reliability of operation of the variable valve train mechanism. Further, manufacturing the helical spline mechanism is difficult, resulting in elevated manufacturing time and cost.
Further, since adjusting valve lift is accomplished by controlling a relative phase angle between the input portion and the output portion, the timing of a maximum lift cannot be changed in some devices.
In the mechanisms which apply a load to one end of the rocker arm (roller) from the camshaft, and then transmit the load to the solid lifter via the output cam from the other end of the rocker arm, since large bending moment acts on the overall rocker arm, the rocker arm needs to have higher strength.